1. Field of the Invention
This invention relates to an image processing and reproducing apparatus. This invention particularly relates to an image processing and reproducing apparatus, in which a plurality of image displaying means are associated with a single image signal output means.
2. Description of the Prior Art
Image processing and reproducing apparatuses have heretofore been used, which comprise an image signal output means for outputting an image signal representing an image, a transmission means for transmitting the image signal having been outputted from the image signal output means, and an image displaying means for reproducing a visible image from the image signal received via the transmission means and displaying the visible image. In the image processing and reproducing apparatuses, predetermined image processing is carried out on the image signal, and the visible image is reproduced from the processed image and displayed on the image displaying means.
For example, image processing and reproducing apparatuses have heretofore been used, in which a radiation image having been recorded on photographic film is photoelectrically read out, an image signal representing the radiation image being thereby obtained, appropriate image processing is carried out on the image signal, and then a visible image is reproduced from the processed image signal. Also, radiation image processing and reproducing apparatuses, in which stimulable phosphors are utilized, have heretofore been used. Specifically, a radiation image of an object, such as a human body, is recorded on a sheet provided with a layer of the stimulable phosphor (hereinafter referred to as a stimulable phosphor sheet). The stimulable phosphor sheet, on which the radiation image has been stored, is then exposed to stimulating rays, such as a laser beam, which cause it to emit light in proportion to the amount of energy stored thereon during its exposure to the radiation. The light emitted by the stimulable phosphor sheet, upon stimulation thereof, is photoelectrically detected and converted into an electric image signal. The image signal is then subjected to appropriate image processing and used for the reproduction of the radiation image of the object as a visible image on a recording material, such as photographic material, or on a display device, such as a cathode ray tube (CRT) display device.
Examples of the image processing principally include frequency emphasis processing (hereinbelow referred to as the USM processing), dynamic range compression processing (hereinbelow referred to as the DRC processing), and gradation processing.
With the USM processing, an unsharp mask image signal Sus corresponding to super-low frequency is calculated with respect to each of picture elements in an original image, and a processed image signal Sproc is calculated with formula shown below. EQU Sproc=Sorg+.beta..multidot.(Sorg-Sus)
wherein Sorg represents the original image signal, and .beta. represents the emphasis coefficient. In this manner, frequency components higher than the super-low frequency are emphasized. The USM processing is disclosed in, for example, Japanese Unexamined Patent Publication No. 62(1987)-62373.
With the DRC processing, in order that portions of an image covering as wide a range of image density as possible can be used, the level of contrast of the portions of the image having a high or low image density or the level of contrast of the entire area of the image is rendered low such that the difference between the highest image density and the lowest image density may become small, i.e. such that the dynamic range of the image may become narrow. In such cases, if the level of contrast is merely rendered low, the problems will occur in that details of the image information in the image region, at which the level of contrast has been lowered, becomes hard to observe. Accordingly, various DRC processing methods for eliminating such problems have been proposed by the applicant in, for example, U.S. Pat. No. 5,454,044 and Japanese Unexamined Patent Publication No. 5(1993) -91276.
In the DRC processing methods proposed by the applicant, image processing is carried out with the formula shown below. EQU Sproc=Sorg+D(Sus)
wherein D(Sus) represents an arbitrary function with respect to the value of the unsharp mask image signal Sus, and Sproc represents the processed image signal. As the function D(Sus), a function, the value of which decreases monotonously as the value of the unsharp mask image signal Sus increases, or a function, the value of which decreases monotonously as the value of the unsharp mask image signal Sus increases and in which the differential coefficient is continuous, is employed. The way, in which the value of the function decreases monotonously, may be set appropriately in accordance with the desired results, which are to be obtained from the image processing.
Also, the calculation of the unsharp mask image signal Sus may be carried out in various ways. In the simplest method of calculating the unsharp mask image signal Sus, the value of the unsharp mask image signal Sus corresponding to each of picture elements in the original image is calculated by averaging the values of image signal components of the original image signal Sorg representing the original image, which image signal components represent the picture elements belonging to a predetermined region surrounding each of the picture elements. An example of the method of calculating the unsharp mask image signal Sus will be described hereinbelow.
FIG. 3 is an explanatory view showing picture elements in an original image (i.e., an image before being processed) and image signal components of an original image signal (i.e., an image signal representing the original image) Sorg, which represent the picture elements. In FIG. 3, dots represent the picture elements, and the symbols, such as S.sub.ij, represent the image signal components of the original image signal Sorg which represent the corresponding picture elements. The value of an unsharp mask image signal Sus.sub.ij for the picture element S.sub.ij, which is located in the middle of the region surrounded by the chained line, is calculated with the formula shown below. ##EQU1## The calculation is carried out for every picture element, and an unsharp mask image signal Sus for the whole image is thereby generated. The values of m and n are determined arbitrarily in accordance with the sampling intervals, with which the original image signal Sorg was obtained, the characteristics of the original image, the kind of the desired image processing, or the like.
The USM processing method and the DRC processing method described above are the most basic USM processing method and the most basic DRC processing method. Besides the USM processing method and the DRC processing method described above, techniques for transforming an original image into multi-resolution images by use of an unsharp mask filter and carrying out image processing by use of a plurality of unsharp mask image signals, which represent unsharp images of respective levels of resolution, have also been proposed. For example, as proposed in U.S. Ser. No. 08/723,313, a filtering process with a filter having a predetermined size is repeated, and multi-resolution images are thereby obtained. Specifically, a plurality of unsharp mask image signals Sus.sub.k, where k=1 to N, are thereby obtained.
As proposed in U.S. Ser. No. 08/723,313, by use of a plurality of unsharp mask image signals described above, frequency emphasis processing can be carried out such that the occurrence of an artifact in a region in the vicinity of an edge in the image may be restricted. In such cases, a processed image signal Sproc can be obtained by carrying an operation represented by, for example, the formula shown below. EQU Sproc=Sorg+.beta.(Sorg).multidot.Fusm(Sorg,Sus.sub.1,Sus.sub.2, . . . , Sus.sub.N) EQU Fusm(Sorg, Sus.sub.1, Sus.sub.2, . . . , Sus.sub.N) EQU ={f.sub.1 (Sorg-Sus.sub.1)+f.sub.2 (Sus.sub.1 -Sus.sub.2)+. . . +f.sub.k (Sus.sub.k-1 Sus.sub.k)+. . . +f.sub.N (Sus.sub.N-1 -Sus.sub.N)}
wherein Sus.sub.k (k=1 to N) represents the unsharp mask image signal, and f.sub.k (k=1 to N) represents the function for converting the band-limited image signal.
Also, as proposed in U.S. Ser. No. 08/723,313, by use of a plurality of unsharp mask image signals described above, dynamic range compression processing can be carried out such that the occurrence of an artifact may be restricted as in the afore said frequency emphasis processing. In such cases, a processed image signal Sproc can be obtained by carrying an operation represented by, for example, the formula shown below. EQU Sproc=Sorg+D(Sorg-Fdrc(Sorg, Sus.sub.1, Sus.sub.2, . . . , SUS.sub.N)) EQU Fdrc(Sorg,Sus.sub.1,Sus.sub.2, . . . , Sus.sub.N) EQU ={f.sub.1 (Sorg-Sus.sub.1)+f.sub.2 (Sus.sub.1 -Sus.sub.2)+. . . +f.sub.k (Sus.sub.k-1 -Sus.sub.k)+. . . +f.sub.N (Sus.sub.N-1 -Sus.sub.N)}
wherein Sus.sub.k (k=1 to N) represents the unsharp mask image signal, and f.sub.k (k=1 to N) represents the function for converting the band-limited image signal.
If specific hardware functions having a high calculation capability are not used, the calculation of the unsharp mask image signals Sus (Sus.sub.k) or the calculation of the processed image signal Sproc, such as the frequency emphasis-processed signal or the dynamic range compression-processed signal, depending upon the unsharp mask image signals Sus, cannot be carried out quickly.
Conventional image processing and reproducing apparatuses are ordinarily constituted such that an image displaying means may be provided with an image processing section and may carry out image processing on an image signal, which has been received from an image signal output means, and the processed image signal may be fed into a CRT display device, or the like. For example, in cases where a plurality of image displaying means are associated with a single image signal output means via a transmission means, each of the image displaying means has heretofore been provided with the image processing section for carrying out the image processing.
However, in the image processing and reproducing apparatus, in which each of the image displaying means is provided with the image processing section for carrying out the complicated image processing, such as the USM processing or the DRC processing, in cases where the image processing is to be carried out quickly, the problems occur in that the cost of the whole apparatus cannot be kept low. Also, in cases where the cost of the apparatus is to be kept low, the problems occur in that a long time is required to carry out the image processing, and the image displaying cannot be carried out quickly. Specifically, in the cases of the USM processing or the DRC processing described above, the amount of calculations to be carried out is very large. Therefore, in order for the USM processing or the DRC processing to be carried out quickly, it is necessary for specific hardware functions, which have a high calculation capability and are expensive, to be used as the image processing section. In cases where the specific hardware functions are employed in each of the plurality of the image displaying means, the problems occur in that the cost of the whole apparatus cannot be kept low. Also, in cases where ordinary hardware functions are employed such that the cost of the apparatus maybe kept low, the problems occur in that a long time is required to carry out the calculations, and the image displaying cannot be carried out quickly.